1. Field of the Invention
The present invention relates to a pantagraph type jack and, more particularly, to a pantagraph type jack which is equipped with an improved dump nut.
2. Description of the Prior Art
The present applicant has already proposed a dump nut, as shown in FIG. 3, in which a nut is composed of a plurality of separate segments 5, these nut segments 5 are disposed in a tapered bore 2 of a casing 1 and are interposed between frictional guide projections 3 so that they can slide back and forth to expand and contract within the tapered bore 2, the tapered bore 2 of the casing is formed with receiving opening at its narrower end and with an insertion opening at its wider end so that it can allow a bolt to be inserted so as to extend therethrough, and the nut segments 5 are always biased to contact the smaller-diameter end of the tapered bore 2 by the action of a compression spring 9. The dump nut thus constructed is enabled to enjoy an outstanding advantage in that the operation of fastening it can be facilitated because it can be advanced without any rotation of the longitudinal path of a bolt 14 by expanding the nut segments 5 thereby separating their internal threads from the external thread of the bolt 14.